How to make a UI image change sprite through a script that is not attached to the UI image itself

I'm trying to get a sprite of a UI image to change when i click on it. Currently what happens is that after i use Application.LoadLevel(0) i can no longer change the sprite of the image.`

 public Sprite MusicOn;
 public Sprite MusicOff;
 public Image image;

 public void OnClickMute ()
 {
     switch (PlayerPrefs.GetInt("Mute"))
     {
     case 1:
         PlayerPrefs.SetInt ("Mute", 2);
         image.sprite = MusicOn;
         audio.mute = false;
         break;
     case 2:
         PlayerPrefs.SetInt ("Mute", 1);
         image.sprite = MusicOff;
         audio.mute = true;
         break;
     }
 }`

What i have noticed is that after the Application.LoadLevel(0) occurs the OnClick event says its missing.

So basically this works fine the first time, however it breaks after reloading